On islanded (or isolated) grids with growing renewable penetrations, grid operators often struggle to maintain system stability. Operators in places as diverse as Ireland, Puerto Rico and Australia frequently rely on inertial response from thermal power plants like coal or gas-fired generators to balance sudden mismatches between supply and demand. However, recent research from Northern Ireland’s Queens University Belfast (QUB) finds that battery-based energy storage can provide inertial response for system reliability much more efficiently, at a lower cost and with substantially reduced emissions than a much larger quantity of thermal generation.
QUB’s research found that just 360 megawatts (MW) of battery-based energy storage could provide the equivalent stabilisation to Ireland’s All-Island electricity system as would normally be provided by 3,000MW of conventional thermal generation. That shift to batteries could save up to €19 million (US$22.5 million) annually and could achieve approximately 1.4 million tonnes of annual CO2 savings.
Inertia: A blink-of-the-eye grid balancing service
Inertia is a system-wide service that responds to fluctuations in electricity frequency in the first fraction of a second of an imbalance between supply and demand – for example, when a power station suddenly drops offline. Traditionally, this stabilising hand has come from the kinetic energy provided by the spinning mass of (synchronous) generators that produce electricity from fossil fuels.
All this occurs well within the first half a second of an issue – literally, the time it takes a human eye to blink. Traditionally the electric power sector has not thought of it as service. It’s just part of the physics of synchronous generators; and we don’t miss something until it’s gone.
As the proportion of energy from (non-synchronous) wind and solar grows this source of traditional ‘analogue’ inertia is in increasingly short supply. The typical solution to this has been to hold back wind and solar output during such times, but this is growing increasingly costly as renewable penetration grows. Let’s face facts: paying not to use zero-fuel cost and zero carbon renewables isn’t a tenable solution in the long run; and would require a significant overbuild of renewable capacity to achieve the same decarbonisation targets.
Energy needed during curtailment is often provided by fossil fuel-powered thermal generators, running when they don’t need to be or running at a higher set point than they need to be, wasting fuel and adding cost.
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